Method and apparatus for dew point evaporative product cooling

ABSTRACT

The present invention relates to a method and an apparatus for providing enhanced indirect evaporative cooling of air, water, fuel, or other fluids while controlling the humidity. The design makes cooling down to the dew point possible without energy input other than the energy to produce the fluid flow needed. The design makes use of stacked composite plates ( 7 ) with channels ( 1, 2 ) for fluid flow between adjacent plates. On opposing surface areas of these plates, there are wet areas ( 4 ) or dry areas ( 3 ). The wet areas ( 4 ) provide cooling by conventional evaporation which is in turn used to cool the fluids in contact with the dry areas ( 3 ). The benefit is controlled heat transfer, which allows selected cooling of fluid flow such that the temperature as low as dew point are reachable.

[0001] Applicant hereby claims benefit of a provisional applicationfiled on Feb. 7, 2000 entitled “Dew point evaporative cooler,” serialNo. 60/180,819, and provisional application filed on Jan. 31, 2001entitled “Indirect Evaporative Cooling Mechanism,” Docket No. 163P.

FIELD ON THE ART

[0002] The present invention relates to methods and apparatus forindirectly cooling a fluid by evaporation and more specifically to amethod and an apparatus for cooling air, or a product other than air, tosubstantially the dew point temperature of the air used in theevaporative cooling.

BACKGROUND OF THE INVENTION

[0003] Indirect evaporative cooling has been used for many years to coolhigh temperature fluids down to near the wet bulb temperatures forcommercial and industrial processes such as refrigeration systems. Theuse of indirect evaporative cooling for direct air conditioning systemshas been commercially available but never commercially viable as provenby the lack of available products on the market at costs that reflectstheir effectiveness.

[0004] The commercially available indirect evaporative cooling systemsuse a two-step process for cooling, indirect evaporative cooling of theair to less than half of the difference between the wet bulb temperatureand then adiabatic cooling to the final temperature. With this processthe temperature is reduced to less than the wet bulb temperature howeverthe humidity is increased significantly. The high humidity limits theiruse to some residential and industrial applications where temperaturenot humidity is a concern.

[0005] There are two major problems with evaporative coolers that are tobe used for supply of air directly for air conditioning: 1) associatedhigh humidity, and 2) high cost of manufacturing.

[0006] There are several prior art indirect evaporative coolers thathave a more thermodynamic efficient indirect evaporative cooling processthan older versions. The prior art has not made it to manufacturing mostlikely due to their lack of understanding of materials needed to realizethe efficiency of the process, the physical design of the apparatus thatrequire at least two separate pieces of equipment and the resultant highcost to manufacture the designs.

[0007] This patent describes a method and apparatus for Dew PointIndirect Evaporative Cooling that utilizes a highly efficientthermodynamic process of heat and mass exchange between air and water,or other volatile fluid, is inexpensive to manufacture, providingtemperatures that approach the dew point temperature of the enteringfluid as opposed to the wet bulb temperature, and with little or nomoisture added to the air.

DESCRIPTION OF PRIOR ART

[0008] Analogy: U.S. Pat. No. 4,002,040 (dated January 1977).Incorporates indirect evaporative cooling over a number of plates andseveral airflow designs that includes using some of the precooled dryair as evaporative air. This design requires a higher-pressure drop dueto the need of the air to enter, pass through, exit an indirectevaporative cooler, then turn around 180 degrees and reenter theindirect evaporative cooler. The wetting system was proposed to beintermittent to help prevent over wetting, but this is difficult inpractice as the drying is dependent on entering air humidity and flowrate. In addition the apparatus will not operate efficiently when eitherover wetted or partially dried out. The materials to build the apparatuswere not discussed, but these affect not only the efficiency but alsothe manufacturability at a cost that could be desirable to consumers.

[0009] Russian Patent No. 2,037,104 (dated Jul. 7, 1991); U.S. Pat. No.5,453,223 (filed Sep. 12, 1994), [though applicant does not admit thevalidity of the U.S. patent, as it was filed more than one year afterthe disclosure was public knowledge]. Disclosed using a square platedesign with cross flow between the plate heat exchange surfaces. Theplates were designed to have wet and dry zones with the opposing sidesof the plate being dry and wet respectively. The wet and dry zones werecreated along the diagonal of the square plate where the air enteredalong a dry surface and proceeded to a wet surface where it departed.Because the plates had wet zones with opposing dry zones, the airpassing in cross flow over them would be indirectly cooled. The designprovided for pre-cooling of the air before entering an evaporativesection and then the flow was split providing either waste heat exhaustair or cooling air to the user.

[0010] This prior art designs have the following disadvantages:

[0011] The existing method and design always increases the absolutehumidity of air used.

[0012] In some applications higher humidity is not wanted.

[0013] The inefficiency of the working air's lower exhaust temperaturesindicating the loss of cooling capacity.

[0014] The unit's inability to cool a product other than air.

[0015] The inability to separate the air streams entering the cooler formore efficient operation. Hot dry air coming out of a dehumidificationprocess, separating from recirculating inside air.

[0016] The unit lacked flow direction in channels causing air mixing andtherefore temperature mixing preventing the greatest possibletemperature differences across a plate. This prevents the lowestpossible outlet temperatures. The lack of flow direction also causesuneven or stagnated flow diminishes the effectiveness of the surfacearea of the plates.

[0017] Inefficient direct evaporative section of cooling air, caused byhaving an impervious surface on one side of the plate.

[0018] The concepts were never put into practical application mostlikely due to their complex design and expensive fabricationrequirements.

[0019] The plates did not have a common wick material making itdifficult to wet the plates.

[0020] The design did not allow for non horizontal wetting of panels orusing natural capillary transporting of water to wet moist surface.

[0021] The design requires higher-pressure drops and thus impairedefficient surface area use.

[0022] The proposed method and apparatus for this invention eliminatesthese disadvantages.

SUMMARY OF THE INVENTION

[0023] The purpose of the method and apparatus for dew point indirectevaporative cooling is to provide the product fluid for example air,water, oil, etc., which is cooled by passing multiple product streamsthrough the invention apparatus to a user. The apparatus uses multipleworking air streams that are first precooled and then passed in crossflow, or counter flow, over an indirect evaporative cooling plate Theworking air streams, by evaporation, take heat from the heat exchangeplate, which provides the interface between the working air and theproduct stream fluid, which in turn takes heat from the product fluid.

[0024] A further object is to obtain lower temperatures when air is usedas the product fluid, by using an adiabatic evaporative section addedafter the indirect cooling dry section, creating an efficient directevaporative process within the same apparatus.

[0025] Due to the thermodynamic cycle in the working air, a furtherrefinement of the apparatus, air can be heated before entering theapparatus in some humid climate conditions to provide added coolingcapacity by providing greater latent heat capacity. This may be done bydirect heat input or by removing humidity from the entering air

[0026] Another object of this invention is to allow the humid workingair exhaust to be used as the product and directed to the user forhumidification of desired area, for example, in the winter, inresidential areas.

[0027] The method and apparatus can be used in conjunction with existingdesiccant dehumidification systems to cool building fresh makeup airtaking advantage of relatively dry and cool building air making a veryefficient process. It can also be used to cool dehumidified buildingrecirculation air.

[0028] The plates in the apparatus are made of a layer of wick materialwith a thin waterproof or low permeability coating in dry zones. Channelguides or corrugated sheets can be used to hold the plates apart andgive direction to the working air and product fluids.

[0029] The plate wick is wetted by wicking, or by natural capillarytransportation of water out of a reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1A is a schematic representation of the flow path of thepresent invention for the first side of plate.

[0031]FIG. 1B is the reverse side of the plate in FIG. 1A.

[0032]FIG. 2A is a schematic representation of the flow path of thepresent invention for the first side of a version of a plate.

[0033]FIG. 2B is the reverse side of the plate shown in 2A.

[0034]FIG. 3A is a schematic representation of the flow channels on thefirst side of a plate as depicted in FIG. 2A.

[0035]FIG. 3B is a schematic representation of a stack of plates.

[0036]FIG. 4A is a schematic representation of a stack of square shapedplates.

[0037]FIG. 4B is a schematic representation of a stack of diamond shapedplates.

[0038]FIG. 5A is a schematic of a plate such as in FIG. 1A with the4^(th) quadrant used as a direct evaporative cooling area.

[0039]FIG. 5B is a view of the reverse side of plate in 5A.

[0040]FIG. 6 is a schematic of a fresh make-up-air drying and coolingsystem for a conditioned space.

[0041]FIG. 7 is a schematic of a recirculation air-drying and coolingsystem for a conditioned space.

[0042]FIG. 8A is a schematic of an apparatus, wherein a plethora ofplates set in a reservoir of water.

[0043]FIG. 8B is an individual plate from FIG. 8A.

[0044]FIG. 9 is a schematic of an apparatus, wherein a plethora ofplates set in a reservoir of water with an apparatus, wherein anevaporative cooling section is included in the apparatus.

[0045]FIG. 10 is a schematic of an apparatus, wherein a plethora ofplates using corrugated sheets to separate them and wherein anevaporative cooling section is included in the apparatus.

[0046]FIG. 11 is a schematic of an apparatus, wherein a plethora ofplates with a feeder wick water distribution system.

DETAILED DESCRIPTION OF THE INVENTION

[0047] The following embodiment as exemplified by the drawings isillustrative of the invention and is not intended to limit the inventionas encompassed by the claims of the application. Method and apparatusfor cooling a product fluid by using ambient air or dehumidified air inan indirect evaporative process that approaches the dew pointtemperature of the entering working airs absolute humidity. In additionthe apparatus can be used to more effectively humidify the air in dryclimates than existing humidifiers on the market. As will be appreciatedby those persons skilled in the art, several major advantages areprovided by the present invention for cooling a product by utilizing asimple, efficient method and apparatus, which has a high efficiency,uses a minimum of energy, consumes a minimum of space and is economicalto fabricate.

[0048]FIG. 1A illustrates one configuration of the top surface of theplate (7) as used in the apparatus. The plate (7) is formed by wickmaterial with a portion having a low permeability material surface, suchas plastic. The low permeability of the plastic layer prevents moisturefrom crossing the plate (7) from one side to the other. The plasticcoating, if a separate layer, is thin and is placed onto the wick layerby painting, by lamination or other suitable means.

[0049] As illustrated in FIG. 1A, the top surface of plate (7) has aportion where the wick material is exposed (4), and a portion with theplastic layer is exposed (3). Additionally, the FIG. 1A shows workingair channels (2), product air channels (1) and channel guides (10). Thewet zone (4) is exposed wick material. The dry zone (3) is the wickmaterial with the impermeable surface. FIGS. 1A, 1B, 2A, and 2B aresegmented into quadrants 51, 52, 53 and 54.

[0050] The configuration as shown is a square. It may be of any suitablestructural shape. For ease of explanation FIG. 3A shows the overallsquare dimensions divided in four quadrants No. 51,52,53, & 54. In thisFIG. 3A quadrants (51) is covered by plastic. Quadrant 52 is covered byplastic over one-half of its area. While 53 is of the wick material andis not covered by plastic. Quadrant 54 in this particular embodiment isomitted from the plate (7).

[0051] There are channel guides (10), see FIG. 1A, located along the topsurface of plate (7). The channel guides (10) are in parallel and spacedthe desired spacing to accomplish the task of confining and directingthe flow of fluids along the surface of plate (7). The flow space isdefined by the adjacent channel guides (10) and the surfaces of adjacentplates (7). Where the channel is bounded by plastic layers on theopposing surfaces of adjacent plates, the channel is designated a drychannel, or product channel (1) in as much as the liquid in the wicklayer is prevented from evaporating into the channel fluid. While thechannel is bounded by the wick layer of adjacent plates (7) the channelis designated as a wet channel or working channel (4) in as much as theliquid in the fiber interacts and evaporates with the fluid or airflowing in the working channel.

[0052] To complete the channel there needs to be a top surface spanningthe channel guides. This is provided by the bottom surface of second ornext plate in an assembly or stack. As can be seen by looking at FIG.2A, the dry zone (3) is in the comparable location to the dry zone onthe bottom surface of the first plate (7). See FIG. 1B and FIG. 2A. Thusthe dry zone of the surface of adjoining plates oppose each other acrossthe space defined by those two plates. Thus the dry channel, or productchannel (1), is created and bounded by plastic coated plate sections.

[0053] In the assembly of plates (7) as shown in FIG. 3B, all odd numberplates will be identical. All even number plates will be identical. Ifwe look at a sample plate as FIG. 2A, divided into quadrants as shownin, and farther remove the fourth quadrant as depicted we will haveplate 1 of the assembly. The channel guides (10) are oriented for thislayer in the designated position. The next plate in the assembly, plate2, also is a square with the fourth quadrant missing but it has itsplastic sheet covering the mirror image of that portion covered in thefirst plate shown in FIG. 2A. When the second plate is stacked onto thefirst plate, resting on the channel guides, there will be space definingchannels.

[0054] For purposes of explaining the working of the assembly, we willdesignate the channels between the first and second plate as product drychannel 61, 62, 63 and 64. 61 and 62 are product dry channels. 63 and 64are the working air wet channels. In quadrant No. 52 the working airpasses over some surface that is plastic coated and some that is not.For channel 63 the majority of the path in the quadrant is over plasticand thus primarily a dry channel. For channel 64 it is primarily overthe wick area and thus a wet channel though it has some plastic or drychannel.

[0055] In the assembly as shown in FIG. 3B the plastic coated section ofthe plate top of the second plate is the mirror image of that portion ofthe first plate. The channel guides are oriented 90 degrees from theorientation of the channel guides on the first plate. With the additionof a third plate channels 71, 72, 73 and 74 are formed and defined bythe channel guides on the second plate, the top surface of the secondplate and the bottom surface of the third plate.

[0056] The flow of the channels in 71, 72, 73 and 74 are cross floworiented to the flow in channels 61, 62, 63 and 64. The channelguides-for the third plate are oriented in parallel to the channelguides on the first plate. With the addition of a fourth plate on top ofthe third plate channels 81, 82, 83 and 84 are formed and defined by thechannel guides on the third plate, the top surface of the third plateand the bottom surface of the fourth plate.

[0057] Channels 81 through 84 are flowing parallel to channels 61through 64 while at the same time being in crossflow orientation tochannels 71 through 74. Using these channel numbers and the orientationas described in FIG. 3A for the quadrants of the plates the interactionand cooling due to the evaporation and particular orientation set forthherein will be discussed and explained.

[0058] For channels 61 and 62 and channels 81 and 82 their flow isentirely in dry channels of the product cooling quadrant 51. Adjacent tothem in the space above plate 2 are the channels 71 and 72, which areworking channels (2) or wet channels. In quadrant 52 over those portionsof channels 71 and 72 that are in the wet area there is an area calledthe pre-cooling section. Through evaporation of the fluid in the wicklike material that are on the floor and ceiling of channels 71 and 72,when the flow is in the pre-cooling area, or later in the productcooling of quadrant 51, the temperature of channel surfaces and thefluids will be lowered.

[0059] The fluids in channels 71 and 72 will have temperatures belowthat of the ambient or starting temperature going into channels 71 and72 caused by the evaporation in the wet portion of channels 63, 64, 83and 84 in quadrant 52. In turn, channels 63, 64, 83, and 84 areprecooled by the evaporation in channels 71 and 72 in quadrant 52. Asthe flow continues down channels 71 and 72 additional evaporation willoccur in quadrant 51 further lowering the temperature of the flow and ofthe adjacent walls of the channel. Because the wick layer on theadjacent plates are the upper and lower walls of channels 71 and 72 andbecause this wick layer is moist from the evaporative liquid there isgood heat transfer through the plates. The product fluid in channels 61,62, 81 ands 82 are then cooled by indirect evaporation.

[0060] The only structure that separates the working channels, 71 and72, from the adjacent spaces and their temperatures, is the plasticlayer on the top surface of the third plate and bottom surface of thesecond plate in quadrant 51. Because this plastic layer is very thin theheat transfer between channels 71 and 72 and the product channels 81 and82 and 61 and 62 is very high, maintaining a small temperaturedifference across the plates. Thus the temperature in channels 61 and 62in the first space layer and channels 81 and 82 in the third space layerare lowered due to the low-temperature in channels 71 and 72 broughtabout by evaporation and pre-cooling. Thus the product flow of fluidentering channels 61 and 62 and channels 81 and 82 has its temperaturelowered during its passage through the channels. Product exits into whathad been the fourth quadrant and are thus and then directed for thedesired use of the product fluid or air.

[0061] The product fluid or air in the second space contained inchannels 73 and 74 are likewise cooled across the plastic barrier by theworking air channels of 63 and 64 and 83 and 84 in the adjacent channellayer's in the stack as illustrated.

[0062] Within quadrant 52, because there is pre-cooling of working fluidin channels 63, 64, 71, 72, 83 and 84 there will be additional coolingin the spaces between the plates 1,2,3 and 4. In channel 71 the firstquarter of the flow is over plastic and thus is a dry channel. There isno evaporation occurring in this section. For the remainder of channels71 in quadrant 52 there is evaporation and thus cooling of the flow andof the adjacent walls. This cooling by channel 71 through heat transferacross the second and third plates that border channel 71 in channels 63and 64 above the first plates space and in channels 83 and 84 above thethird plates space precools the air. This cooling due to channel 71occurs in the early part of the flow in 63, 64, 83 and 84. Thus the flowin these four channels is precooled, without adding humidity, before itcommences to be cooled by evaporation within its own channel.

[0063] Similar pre-cooling occurs in channel 71 however channel 72 hasmore cooling because there is more plastic covering channel 72 inquadrant 52. The flow in channel 72 is precooled by the flow occurringin 63, 64, 83 and 84. Because there is more plastic in channel 72 thereis more pre-cooling from these adjacent channels.

[0064] The pre-cooling occurring in quadrant 52 lowers the temperaturesof all the working air before entering the product cooling section inquadrant 51 and 53.

[0065] The embodiments as shown in FIGS. 1, 2, 3 and 4A are of a squareconfiguration of plates (7). There are alternatives, among them adiamond shape such as shown in FIG. 4B. The selection of a square shapeor diamond shape would be determined by the design decisions as furtherexplained.

[0066] A diamond shape has the advantages of having the working fluidflowing relative to the product fluid at an angle other that ninetydegrees. Rather than being oriented at right angles to the adjoiningfluid flow it is more of an obtuse angle. The flow is more counter flowthan cross flow. As the angle of orientation moves beyond 90 degrees thearea of interaction of the product flow and the working fluid in theadjoining layer increases. Thus the working fluid while becoming coolerthrough evaporation has more time to interact with the product fluid.The product fluid is given more time to cool by heat transfer.

[0067] At the end of the working air channel the working air temperatureis lower due to its longer exposure to the evaporative surface in thewet zone. In the diamond shape, there is a greater proportion of thearea of the plate (7) on the perimeter, in as much as the square shapehas more interior area. Thus the diamond shape gives proportionatelymore area on the perimeter, area that is cooler due to the ends of theworking air channels are at the perimeter. In any heat transfer surface,the amount of area and the differential temperatures in these areas (allother things being equal) will affect the amount of heat transfer thatwill occur. In the diamond shape the coolest part of the working fluidis at the perimeter, and inasmuch as the diamond gives more area at theperimeter, the diamond gives more proportion of its area to heattransfer where the temperature of the working flow is the coolest. Thusthe diamond shape gets greater heat transfer because of the distributionof the area in the diamond puts more of the coolest area at theperimeter, where the product fluid has the largest amount of area tointeract with it. Thus there will be more area for heat exchange for thetwo flows and thus to have the sensible heat transfer across the plasticsurface (3).

[0068] An additional feature of the diamond shape that accentuates theheat transfer more than what occurs in the square shape, is thecounterflow. Flows being more counter flow than cross flow, the gradientof temperature as it decreases along the working air (2) channel, putsthe lowest part of the temperature in the working channel, across theheat transfer surface from the product air (1). Thus the heatdifferential is greatest and the heat transfer will be the greatest.Though this same effect will occur in square shapes, the square havingmore interior area does not get the same quantity of heat transfer.

[0069] Another advantage of a diamond shape when used in an uprightorientation (See FIGS. 8A and 8B) is the advantage of lower verticaldistance for plates when the diamond is oriented with its long axishorizontal to the ground. If the plates (7) in their assembled state arevertical or at an angle of orientation or slope the lower edge may beimmersed in a reservoir of evaporating fluid. The wicking function ofthe wick layer transports the evaporating fluid from the reservoirupward to the upper reaches of the wick layer. If the plates shape is adiamond shape this vertical height that must be wicked in order to wetthe upper reaches of the wick layer will be lower. The wicking can occurover longer distances, more efficiently, the more horizontal the platesare.

[0070] The advantages of a square shaped plate is in its compactness. Asdiscussed previously, a square, over a diamond, creates the smallestfootprint. More of the area is in the interior. The square shape then isbest where compactness is essential.

[0071] In addition to the shape, the omission of the 4^(th) quadrant(54)as shown in FIG. 3A has advantages. By removing the 4^(th) quadrant areduced pressure drop for the fluid flow for the product air (1) isachieved. The product air is cooled by the adjacent working air (2). The4^(th) quadrant would merely place adjacent layers of product air(presumable at the same temperature) next to each other. No gain in theproduct temperature is had. By omitting the 4^(th) quadrant less energyis expended in the passage of the product through these areas of theproduct channels, as the restricted channel is shorter.

[0072] An alternative design decisions may dictate that quadrant 4 (54)not be omitted but rather kept as an evaporative area for the productflow, see FIG. 5A. This added area of direct evaporative cooling for theproduct air (1) that is previously came through the product air channels(3) will give these advantages: there will be added cooling to theproduct air and some degree of humidity will be added to the productair. The addition of direct evaporation cooling may be necessary in someapplications to lower the temperature.

[0073] In some environments the main feature or function of the withindesign may be to add humidity. This can be accomplished by the apparatusas shown in FIG. 3A by making use of the exhaust product which hasincreased humidity over typical evaporative humidifiers. Additionallythe use of direct evaporative channels after the product channel can beused to add humidity to the product air such as in FIG. 5A.

[0074] The exact mix of humidity to add to the product air can bealtered by design decisions of the amount of direct evaporative coolingadded to the product channel or by mixing the exhaust working air insome proportion with the dry cooler product air by use of baffles orother means.

[0075] In addition the ability to add humidity and at the same timecontrol the temperature of the end product mixture enables the user toadjust humidity and temperature independently to accomplish the targetconditions. This apparatus allows the user to adjust the humiditywithout having to also adjust the temperature by an outside heat sourcein conditions where higher humidity is desired but not lowertemperature.

[0076] The apparatus by an additional feature can manipulate the latentheat capacity of the working fluid to accomplish a more efficientcooler. By adding heat to the working air (2), additional latent heatcapacity of the working air and additional evaporation capacity resultsto the system. If the working air has humidity above 0.0011 to 0.0014pounds of water per pound of air (wherein the variation is dependentupon the elevation above sea level) the adding of heat to the workingair will aid in the heat transfer mechanism. Above this level ofhumidity the addition of sensible heat causes a much greater increase inthe latent heat capacity of air. This is a benefit to the coolingprocess. This added latent heat capability gives the working air greatercapacity, which in turn gives the system greater capacity to cool downthe temperature through the evaporative process.

[0077] The flow of fluids, working air (2) or product air (1), can beaided by common mass transfer devices such as fans pumps or otherdevices common in industry. To aid in the efficiency of the system andits design the indirect evaporative cooler is enhanced if the workingair (2) has a pressure drop at its exhaust which induces the flow of theworking air through the working air channels (17). By producing anegative pressure differential across the working air channel theevaporative process in the working air channel will be enhanced as lowerpressure aids evaporation.

[0078] Desiccants can also be used in the system as shown in FIGS. 6 and7. The benefits to the indirect evaporative cooler are in enhancedefficiencies of the evaporative process, control of the humidity of theworking or product air, and the use of the by product of the heatgenerated during dehumidification to increase the latent heat capacityof the working air in the evaporative process In viewing FIGS. 6 and 7the desiccants wheel is illustrated (13). In FIG. 6 outside air is firstdrawn through and dehumidified by the desiccant wheel. Thedehumidification raises the temperature of the dehumidified air due tothe heat occurring by extracting the water from the outside air. In FIG.6 the dehumidified air is used as the product air, in order to controlthe humidity and yield cool dry air as product (1). In FIG. 6 theworking air is recirculated air from the condition space (12) which isalready dry and thus a larger capacity for the evaporative process forthe cooling.

[0079] As shown in FIG. 7 the air from the conditioned space isrecirculated. In this embodiment the recirculated air is used for boththe product air and the working air. After recycling, the working air isexhausted and thus there is a net loss of air for circulation. To makeup for this loss, outside air is used to supplement the system air.Before use the outside air may have to be dehumidified. After goingthrough the desiccant wheel and becoming dehumidified this combinationair is fed into both the product (16) and working (17) channels. Theexhaust of the working channel (17) is exhausted to the outside and theproduct channels (16) in sent to the conditioned space (12).

[0080] The dissipate of the desiccant system usually requires the use ofthe heat exchanger system to redirect or dissipate the heat caused bythe dehumidification step. However in the subject design the heatgenerated by the dehumidifier is used to enhance the evaporative processby going to the working air stream. Thus rather than having to removeheat from this dehumidified air the heat gives added efficiency andcapacity to the system.

[0081] The system of wetting the wick material in the plates (7) byevaporating fluid can be accomplished by pure wicking from a low pointof the wick material immersed in a reservoir or by distributing theevaporating fluid by means of feeder wick that is positioned andinterface with the wick material on the plates. FIG. 11 illustrates afeeder wick where evaporating fluids are distributed by way of hoses ortubes to the desired location. From the tube the evaporating fluidenters the feeder wick which fits in a hole in the plates. The outeredge of the wick material on the feeder wick interfaces with the insidesurface of the holes in the plates and the wicking layer on the plates.The evaporating fluid fed by way of the tube to the feeder wick and thenexits the tube through porous openings or holes into the feeder wickmaterial. This feeder system prevents the pooling of liquid which caninhibit the evaporation process due to surface tension of fluids.Additionally the wicking methods do not require as much energy totransport the fluid. Thus energy cost will be saved.

[0082]FIGS. 8A, 8B, and 9 illustrate the reservoir system where theplates are vertical or in a sloped position with their lower edgeimmersed in the reservoir holding the evaporating fluids. As theevaporation takes fluids from the wick material the wicking from thereservoir replenishes that liquid for subsequent evaporation. In orderto aid in the wicking the plates cannot be overly tall.

[0083] This may be addressed by the use of a diamond shape as previouslydiscussed rather than a square shape. Alternately the plates may beelevated at an angle rather than vertical. This minimizes the amount ofgravity that must be overcome to wet the uppermost area of the wickmaterial.

[0084]FIG. 10 illustrates an assembly where the individual plates(without the separate channel guides (10) are separated by corrugatedinserts. These inserts maintain the separation and also act as thechannel guides for the flow of product air and workign air. The insertsare preferred to be of an impermeable material such as plastic or resinimpregnated cellulose or paper so that in the wet channel thepurportrating liquid won't be in the inserts.

We claim the following:
 1. A method to provide indirect evaporativecooling while controlling humidity of the cooled product air by havingthree plates in parallel: a) forming a first space and second spacebetween adjacent plates with the middle plate being a common plate toboth spaces; b) wetting opposing surfaces of the adjacent plates; c)keeping some surface areas of opposing surfaces dry d) passing air inthe first space in two types of channels, working channels and productchannels; e) passing air in the second space in working channels andproduct channels in cross flow to the flow in the first space channels;f) controlling the humidity in the product channels by the amount of wetsurfaces the product air is exposed to in the product channels; and g)cooling the air in the product channels by the dry surfaces being cooledby heat transfer across the common plate in this area and theevaporation cooling on the opposite surface of the common plate in theadjoining space that is occurring in a wet area of a working channel. 2.The method of claim 1 wherein pre-cooling occurs in each space in asection where working channels are on both sides of the common platehaving dry areas and wet areas having equal area. The pre-coolingsection having the dry area occurring first in the working channelhaving the transitive to a wet area occurring on a diagonal to thedirection of flow in the working channel having the orientation of theworking channel dry area in a first spacing being opposite from the dryarea of the working channel of the second space such that the commonplate dry area in the first space is opposite the wet area of the commonplate in the second space pre-cooling of the working air in the secondspace by heat transfer from the first space and pre-cooling of theworking air in the first space by heat transfer from the second space.3. A method according to claim 1 wherein after the product fluid, forexample air, has passed through the product cooling section it passesover a wet surface.
 4. A method according to claims 1-2 wherein theproduct fluid may have it's own pump, fan or any fluid moving device. 5.A method according to claims 1-3 wherein the working air is heatedbefore entering the pre-cooling section.
 6. A method according to claim1 wherein the humid working air exhaust becomes the product and isdirected to the user for humidification of desired area.
 7. A methodaccording to claim 1 wherein outside ventilation air is used as theproduct fluid for the user in, for example, a conditioned space and ispassed through a solid or liquid desiccant dehumidifier; this productair is then cooled by passing its two streams over the dry side of twoproduct cooling sections, and then is directed to the user;simultaneously the exhaust air from conditioned space and/or outside airthat has passed through a solid or liquid desiccant dehumidifier is usedas the working air, that then passes by two streams through thepre-cooling section, is then directed straight across the productcooling section and then is exhausted out.
 8. A method according toclaim 1 wherein all or a portion of the inside recirculation air is usedas a product fluid for the user in, for example, a conditioned space andis passed through a solid or liquid desiccant dehumidifier; this productair is cooled by passing its two streams over the dry side of twoproduct cooling sections and then is directed to the user;simultaneously outside air and in some cases all or a portion of thesame recirculation air from conditioned space, after its passing throughthe desiccant dehumidifier, is used as the working air, that then passesby two streams through the precooling section, is directed straightacross the product cooling section and then is exhausted out.
 9. Anapparatus for indirect evaporative cooling comprised of at least twoplates in parallel, each plate having two surfaces wherein: a) at leastpart of one of the surfaces is impermeable to the fluid used forevaporation, b) the plates are made of a material that has a wick likecapability that transports the liquid used for evaporation to the areasof the plates where evaporation is to occur and once there allows theliquid to evaporate, c) the impermeable areas are thin so as to allowfor heat transfer, d) the opposing surfaces of adjoining plates are oflike surface permeability, e) the evaporation occurs in the areaswithout the impermeable surface and cools the surface and the workingair, f) the cooler temperatures due to the evaporation is in heattransfer contact with the impermeable surface and the product air thatis in contact with this surface. The apparatus of claim 1, has channelguides, working air channels, and product air channels to direct theflow in a desired path.
 10. The apparatus of claim 2 where the shape isof a diamond.
 11. The apparatus of claim 2, where the shape is square.12. The apparatus of claim 1 where the impermeable surface is created bya plastic coating on the wick material.
 13. The apparatus of claim 1where the plates of the stack have impermeable surfaces on the productchannels to inhibit any direct evaporation occurring.
 14. The apparatusof claim 1 where the working channel have some areas of impermeablesurface.
 15. The apparatus of claim 1 where the shape has one partremoved.
 16. The apparatus of claim 1 where the shape uses the forthquadrant to have direct evaporative cooling of the product air after ithas been cooled by the indirect cooling.
 17. The apparatus of claim 1where the plates are fed the liquid for evaporation by feeder wicks. 18.The apparatus of claim 1 where the plates are sloped with the lower edgefed liquid for evaporation by a reservoir.
 19. The apparatus of claim 1where the working air is heated before it is used in the working airchannels.
 20. The apparatus of claim 1 where the working air isdehumidified before it is used in the working air channels.
 21. Theapparatus of claim 1 where flow of working air and product air betweenadjoining channels separated by a plate are in cross flow.
 22. Theapparatus of claim 1 where flow of working air and product air betweenadjoining channels separated by a plate are more counterflow.
 23. Theapparatus of claim 1 where the working air is taken from the exhaustafter the product air was used.
 24. The apparatus of claim 1 where thesome working air exhaust is added to the product air to accomplish thedesired temperature and humidity.
 25. An apparatus of claim 2 wherein:a) one of the quadrants with only working air channels has one half ofeach quadrant surface covered with plastic, such that the working airenters one channel; b) the channel is in the non evaporative portion ofthe channel and gets precooled by adjacent layers; c) the working airchannels also in the quadrant that have evaporative cooling in area oftheir channels; and d) the channels interface with the first channelplastic surface.
 26. A method to provide indirect evaporative coolingand to control the humidity by having at least two plates with twosurfaces wherein there is: a) wetting on opposing surfaces of theplates; b) keeping some surfaces areas of the opposing surfaces dry; c)passing air between the plates; d) controlling the humidity by varyingthe amount of wet surfaces to which the air is exposed; and e) coolingthe air over the dry areas by heat transfer by having evaporationoccurring on the opposite side of each plate in the area.